Microphone diaphragm including spacer means between diaphragm and voice coil



y 19, 1970 PAUL-FRIEDRICH WARNING 3,513,270

MICROPHONE DIAPHRAGM INCLUDING SPACER MEANS BETWEEN .DIAPHRAGM AND VOICE COIL Filed May 9, 1966 a Sheets-Sheet 1 INVENTOR M- wn/7 ATTORNEY May 19, 1970 PAUL-FRIEDRICH WARNING 3, MICROPHONE DIAPHRAGM INCLUDING SPACER MEANS BETWEEN Filed-May 9, 1966 .DIAPHRAGM AND VOICE COIL z Sheets-Sheet 2 INVENTOR ATTORNEY United States Patent 0 3 513 270 MICROPHONE nIAPnTRAa/i HNCLUDING srncna MEANS BETWEEN DIAPHRAGM AND VUICE COIL Paul-Friedrich Warning, Bissendorf, Hannover, Germany,

assignor to Sennheiser Electronic, Wennebostel, Germany Filed May 9, 1966, Ser. No. 548,445 Claims priority, application Germany, May 8, 1965, 1,266,814 Int. Cl. HtMr 9/04 US. Cl. 179115.5 18 Claims ABSTRACT OF THE DISCLOSURE A microphone diaphragm including a central diaphragm portion, an annular linking portion surrounding this central diaphragm portion, an outer attaching portion surrounding the linking portion integral with the latter, a

voice coil, and at least two spacer means secured to the voice coil. Said spacer means extending between and interconnecting the intersection line of the diaphragm and the front edge of the voice coil so as to provide openings between the intersection line and the front edge of the voice coil permitting sound and air to pass from the space rearwardly of the linking portion to the space rearwardly of the central diaphragm portion.

It is known to subject both sides of a membrane in a pressure gradient microphone to the action of sound waves. Thereby one side of the membrane, usually the front side, is directly subjected to the sound waves, whereas the other side, usually the rear side, is reached by the sound waves over acoustic impedances. Such impedances are for instance constituted by the air gap in which the voice coil swings, or by other openings which extend through a central pole shoe of the magnet arrangement which cooperates with the voice coil.

Such constructions, however, have considerable disadvantages. If the air gap in which the voice coil swings is used as a sound passage, the width of this air gap has to be considerably increased above the optimum width for the magnetic circuit to avoid excessive acoustical losses in this air gap. If, on the other hand, openings in the central pole shoe are used for providing a sound passage, the construction of the magnets and the yoke parts cooperating therewith becomes complicated and expensive.

A construction is also known which aims to avoid the disadvantages above-described and such construction is disclosed in the US. Pat. No. 3,132,713. In this construction the sound passages from the space rearwardly of the central portion of the membrane to the space rearwardly of the annular linking portion surrounding the central portion of the membrane are formed by trough-shaped channels, which, viewed from the rear face of the membrane, extend in the form of radial corrugations into the curved central portion and into the curved linking portion of the diaphragm. The space behind the curved linking portion of the diaphragm is then connected in a known manner over acoustic impedances to the source of sound. This construction disclosed in the afore-mentioned patent has however the disadvantages that the corrugations do not only form sound passages, but that the corrugations form also mechanical bridges so that the connection between the central diaphragm portion and the surrounding annular linking portion is reinforced in such a manner so that the rigidity of the whole diaphragm is considerably increased, which for certain applications is highly undesirable.

It is an object of the present invention to overcome the disadvantages above-described in microphone diaphragm constructions of the type mentioned.

It is an additional object of the present invention to provide in a microphone diaphragm with a voice coil a proper connection between the diaphragm per se and the voice coil in such a manner that air and sound may freely pass between the rear face of the diaphragm and the front edge of the voice coil connected thereto from a peripheral linking portion of the diaphragm to a central portion thereof and in which the connection is made in such a manner so as to not unduly increase the rigidity of the diaphragm.

It is a further object of the present invention to provide a construction as mentioned above which can be manufactured in a simple and efficient manner so that the whole arrangement may be produced at a very reasonable cost.

With these and other objects in view, the microphone diaphragm according to the present invention mainly comprises a central diaphragm portion, and an annular linking portion surrounding the central diaphragm portion integral therewith. At least one, preferably both, of the aforementioned portions are curved in cross-section and intersect each other along an intersection line. The portions are curved in such a manner so that tangents at any point of said intersection line to outer surfaces of said portions include an angle different from zero. The diaphragm includes further an annular attaching portion surrounding the linking portion and integral with the latter, a voice coil having a front edge rearwardly spaced from the aforementioned intersection line and at least two spacer means extending between and interconnecting the intersection line and the front edge of the voice coil so as to provide openings between the intersection line and the front edge of the voice coil permitting sound and air to pass from the space rearwardly of the linking portion to the space rearwardly of the central diaphragm portion.

The diaphragm is formed from a very thin metal or plastic material foil and the various portions of the foil are formed by a stamping or drawing operation. According to the method of the present invention the spacer means are integrally formed with the other portions of the diaphragm and the forming of the spacer means is performed by stamping, drawing or a similar operation substantially in one operation with the formation of the other portions of the diaphragm. This formation of the spacer means directly out of the material of the diaphragm will insure that the structure of the whole diaphragm remains substantially uniform, which in turn considerably increases the quality of the microphone.

If it is desired to provide between the intersection line and the front edge of the voice coil openings of relatively large height, each of the spacer means may comprise a portion integral with the diaphragm portions and an additional spacer member connected to the rear end of this portion of the spacer means and the front edge of the voice coil. The connection of the additional spacer member to the rear end of the portion of the spacer means integral with the diaphragm and the front edge of the voice coil may be made by cementing, welding, or, when the voice coil is made from plastic material, by heat sealing. Regardless how the connection is made, this connection will be spaced from the actual diaphragm so that the structure of the latter will not be detrimentally effected by any of the afore-mentioned connections.

It is also within the scope of the present invention to provide a damping or impedance material in the aforementioned openings, at least partly closing the same. Such damping material may consist of gauze, fabric or similar material.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic longitudinal cross-section through one possible embodiment of a microphone in which a microphone diaphragm with a voice coil according to the present invention is used;

FIG. 2 is a cross-sectional view drawn to a slightly enlarged scale of the diaphragm according to the present invention and the voice coil connected thereto;

FIG. 3 is a partial cross-sectional view of the arrangement shown in FIG. 1;

FIG. 4 is a cross-sectional view similar to FIG. 2 and showing a modified arrangement;

FIG. 5 is a cross-sectional view similar to FIG. 2 and showing a further modification according to the present invention, the section being taken along line 55 of FIG. 6;

FIG. 6 is a top view of the arrangement shown in FIG. 5;

FIG. 7 is a top view similar to FIG. 6 showing a further modification;

FIG. 8 is a partial cross-sectional view of the arrangement shown in FIG. 7 and drawn to a greatly enlarged scaletand FIG. 9 is a cross-sectional view similar to FIG. 8 and showing a further modification.

FIG. 1 schematically illustrates one possible construction of a microphone in which the diaphragm construction and a voice coil connected thereto according to the present invention may be used. The construction shown in FIG. 1 is not only strictly schematic, but it is also emphasized that the diaphragm construction with the voice coil connected thereto according to the present invention, may be used also in microphone constructions differing from the microphone construction as shown in FIG. 1. The microphone illustrated in FIG. 1 is a pressure gradient microphone having a diaphragm D according to the present invention and a magnet construction M cooperating therewith. The diaphragm D has a central diaphragm portion which may be in the form of a spherical segment or of similar curved dome-shaped construction, an annular linking portion 2 likewise of curved cross-section, and an outer annular connecting portion 3 which may be located in one plane, as shown in FIG. 1. The aforementioned portions are integral with other and the central portion 1 intersects the annular linking portion 2 along a preferably circular intersection line 4. The voice coil 6 of known construction and of a diameter substantially identical with the diameter of the intersection line 4 is arranged so that the front edge 6' thereof is rearwardly spaced from the aforementioned section line and the front edge of the voice coil is connected at spaced portions thereof to the intersection line by spacer means 5, in the manner as will be described in detail later on, so as to provide a plurality of openings 7 through which air and sound may pass from the space 2' rearwardly of the linking portion of the diaphragm to the space 1' rearwardly of the center portion thereof. The magnet system cooperating with the voice coil 6 comprises a central pole shoe 15, an annular pole shoe 16 concentric with the central pole shoe 15 and having an inner surface radially outwardly spaced from the outer surface of the central pole shoe 15 so as to provide between the two surfaces an annular air gap 13 in which the voice coil 6 may swing. Arranged rearwardly of the central pole shoe 15 and abutting with one end thereof against the rear face of the latter is a central magnet 17 having a north pole indicated with the letter N, and a south pole indicated with the letter S. A cup-shaped member 18 of magnetizable material closes the magnetic circuit between the central magnet 17 and the annular pole shoe 16. The cup-shaped member 18 is located in a housing 19 which is formed with a plurality of, for instance substantially L-shaped, passages 19 which communicate at their upper ends thereof, as viewed in FIG. 1, with passages 16' passing through the annular pole shoe 16 so that air and sound waves may pass through the passages 19 and 16 into the space 2' rearwardly of the linking portion of the diaphragm. If necessary, the passsages may be partly closed with acoustic resistances, for instance, gauze or the like. The cup-shaped member 18 is provided adjacent the annular pole shoe 16 with a plurality of transverse openings 18 therethrough which provide communication between the passages 19' and the space 20 between the inner surface of the cup-shaped member 18 and the outer surface of the central magnet 17. The openings 18 are preferably filled with material providing an acoustic impedance. The acoustic impedance in the openings 18 and in the passages 19' serve in a known manner to provide a phase shifting for the sound entering through the passages 19'. This phase shifted sound then passes through the openings 16 in the annular pole shoe 16 into the space 2 and from there through the openings 7 into the space 1' rearwardly of the central membrane portion 1. The voice coil 6 which is held by the spacer means oscillates in the air gap 13 which communicates at the lower end with a small space 22 which is acoustically sealed by a non-magnetic disc 21 against the space 20.

FIG. 2 illustrates in cross-section and at an enlarged scale the diaphragm according to the present invention and the voice coil attached thereto. The diaphragm per se includes as mentioned above, a central preferably domeshaped diaphragm portion 1, an annular linking portion 2, likewise curved in cross-section, and in the same direction as the central portion 1, and intersecting the latter along an intersection line 4 which is preferably in the form of a circle. The portions 1 and 2 are curved in such a manner that tangents 1a and 2a (FIG. 3) directed from any point of the intersection line 4 to outer surfaces of the aforementioned portions include an angle a greater than Zero. An annular attaching portion 3' surrounds the linking portion 2 integrally formed therewith, by means of which the diaphragm may be attached to the annular pole shoe 16, as shown in FIG. 1. A voice coil 6 of known construction has a front edge 6 rearwardly spaced from the intersection line 4. Spacer means 5 extend between the intersection line 4 and the front edge 6' of the voice coil which is attached to the front edge 6' thereof to the rear ends 5' of the spacer means by being cemented or welded thereto. According to the present invention the spacer means 5 are preferably formed integrally with and from the same material as the diaphragm.

The curved portions of the diaphragm are formed by stamping or embossing a flat disc between appropriate die members and the female die member provided with cavities into which the curved portions of the central diaphragm portion 1 and the annular linking portion 2 are pressed by corresponding portions of a male die member are formed with a plurality of small prongs, corresponding to the number of spacer means 5 to be provided in the diaphragm, to press small portions of the latter located along the intersection line 4 into corresponding small cavities of the other die member so as to form the spacer means 5 during forming of the other portions of the diaphragm integral with the diaphragm portions.

Another way of forming the spacer means according to the present inventaion may especially be used when the diaphragm is formed from a thin plastic foil. According to this modified method the prongs on the female die member are omitted and the small cavities in the male die member in which the spacer means are to be formed are connected to a source of suction so that the portions of the diaphragm along the intersection line 5 at which spacer means are to be formed are drawn by suction into the small cavities of the male die member. In this method the diaphragm is preferably heated at least locally at the portion thereof at which the spacer means are to be formed. The last mentioned method is especially advantageous in that tearing of the extremely thin diaphragm at the portions at which the spacer means are formed is positively prevented by this method. The height of the spacer means 5 thus formed is in the order of 0.2-0.5 mm.

The spacer means 5 provide between the intersection line 4 and the front edge 6' of the voice coil 6, the openings 7 through which air and sound may pass in the manner as described above from the space rearwardly of the annular linking portion 2, of the diaphragm to the space rearwardly of the central portion 1. If desired the opening 7 may be covered in any convenient manner with acoustic impedance material such as gauze, fabric or the like.

FIG. 4 shows an arrangement similar to that abovedescribed in connection with FIG. 2. The arrangement illustrated in FIG. 4 differs from the above-described arrangement in that additional spacer means 8 are provided between the rear ends 5' of the spacer means integrally formed in the above-described manner with the diaphragm portions and the front edge 6' of the voice coil 6. This provides openings 7 having a greater height than the openings 7 shown in FIG. 2. The additional spacer means 8 are connected at opposite ends thereof to the rear ends 5' of the spacer means 5 and to the front edge 6 of the voice coil 6 by cementing, welding or heat sealing. The arrangement in FIG. 4 differs also from the arrangement in FIG. 2 in that the attaching portion 3 does not extend in a plane, but the attaching portion 3 is shown in this case as a cylindrical portion extending rearwardly from the outer edge of the linking portion 2. Of course an attaching portion 3' as shown in FIG. 4 may also be used with the spacer arrangement of FIG. 2 and vice versa.

In the embodiments shown in FIGS. 2 and 4 two spacer means are provided which are arranged diametrically opposite to each other.

FIGS. 5 and 6 illustrate a slightly different arrangement in which four spacer means are provided for maintaining the voice coil -6 rearwardly spaced from the intersection line 4. As can be seen from these figures, two of the spacer means, that is the spacer means 5a which are arranged diametrically opposite to each other are substantially cupshaped, whereas the spacer means 5b, which are likewise arranged diametrically opposite each other and circumferentially displaced through an angle of 90 with regard to the spacer means 5a, are elongated or trough-shaped to extend along a segment of the intersection line 4 and each of the spacer means 5b may extend through an are having a length of 2-15 mm. Of course instead of providing alternating cup-shaped and trough-shaped spacer means 5a and 5b, it is also possible to use only troughshaped spacer means or only cup-shaped spacer means.

An arrangement showing only cup-shaped spacer means is illustrated in FIGS. 7 and 8. As best seen from FIG. 7, a relatively great number of cup-shaped spacer means 5a are arranged preferably uniformly spaced from each other, along the intersection line 4. The spacer means 5a may be circumferentially spaced from each other a distance between 3 and 20* mm. and each of the cup-shaped spacer means 5a has a maximum diameter less than 1 mm. at the bottom end thereof. The height of the spacer means is as mentioned above in the order of 0.2 to :5 mm., preferably about 0.3 mm.

The diaphragm according to the present invention and the spacer means integrally formed therewith are made from thin metal or plastic material and preferably from plastic foils of polyvinyl chloride. However, plastic foils of other material such as for instance Mylar or other plastic material may be used. The thickness of the plastic foils used may be in the order of 20 microns.

In order to reinforce the hollow spacer means a or 511, the interior of the latter may be at least partly filled with a reinforcing material 9 (FIG. 9). The reinforcing material is preferably in the form of a self-hardening material, preferably comprising a binder material adapted to harden by reaction with a hardener and a hardener for the binder material such as for instance an epoxy resin hardener system. Such a mixture hardens substantially without shrinking after a certain time, depending on the chemical composition of the mixture and the tempera ture. This provides for a very strong and very light reinforcing material.

The arrangement above-described and the manner of forming the spacer means has the advantage that the structure of the foil material will not be changed during forming of the spacer means and that the flexibility of the diaphragm will substantially not be influenced by the spacer means provided. An undesirable stiffening of the diaphragm is avoided and the mass of the diaphragm is practically not increased by the spacer means. Nevertheless, the arrangement according to the present invention provides by the relatively large openings 7 proper communication between the space rearwardly of the linking portion of the diaphragm and the space rearwardly of the central portion thereof. The air gap 13 in which the voice coil 6 swings need not be increased with the arrangement according to the present invention and the width of the air gap may be held to a minimum best suited for the magnetic flux.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of microphone dia phragms, differing from the types described above.

While the invention has been illustrated and described as embodied in a microphone diaphragm with a voice coil, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitutes essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A microphone diaphragm, comprising, in combination, a central diaphragm portion; an annular linking portion surrounding said central portion, at least one of said portions being curved in cross section, said central diaphragm portion and said annular linking portion being integral with each other and intersecting each other along an intersection line and the curved portion being curved in such a manner that tangents at any point of the intersection line to outer surfaces of said portions include an angle different from zero; an outer attaching portion surrounding said linking portion integral with the latter; a voice coil having a front edge rearwardly spaced from said intersection line; and at least two spacer means projecting beyond said intersection line in a direction away from said diaphragm portions and interconnecting said intersection line and said front edge of said voice coil so as to provide openings between said intersection line and the front edge of said voice coil permitting sound and air to pass from the space rearwardly of the linking portion to the space rearwardly of the central diaphragm portion.

2. A microphone diaphragm as defined in claim 1, wherein each of said openings extends in direction of said intersection line a distance greater than each of said spacer means.

3. A microphone diaphragm as set forth in claim 1, wherein said intersection line is a circle.

4. A microphone diaphragm as set forth in claim 1, wherein said spacer means are from the same material and integral with said diaphragm portions.

5. A microphone diaphragm as set forth in claim 1, wherein each of said spacer means comprises a portion integral with said diaphragm portions and having a rear end facing said front end of said voice coil, and including additional spacer members respectively connected to said rear ends of said portions of said spacer means and the front edge of said voice coil.

6. A microphone diaphragm as set forth in claim 1, wherein said intersection line is a circle, wherein said spacer means are from the same material and integral with said diaphragm portions, and wherein each of said spacer means extends circumferentially through a small arc of said intersection line.

7. A microphone diaphram as set forth in claim 6, wherein said spacer means are arranged diametrically opposite each other.

8. A microphone diaphram as set forth in claim 7, wherein each of said spacer means extends through an arc of a length of 2-15 mm.

9. A microphone diaphragm as set forth in claim 4, wherein each of said spacer means is hollow and has an open end facing away from said voice coil.

10. A microphone diaphragm as set forth in claim 9, wherein more than two spacer means are provided arranged along said intersection line circumferentially spaced from each other a distance of 3-20 mm.

11. A microphone diaphragm as set forth in claim 9, wherein each of said spacer means is substantially cupshaped having a maximum diameter less than 1 mm.

12. A microphone diaphragm as set forth in claim 9, wherein each of said spacer means has a height in the order of 0.2-0.5 mm.

13. A microphone diaphragm as set forth in claim 9, and including reinforcing material at least partly filling said hollow spacer means.

14. A microphone diaphragm as set forth in claim 13, wherein said reinforcing material is a self-hardening material.

15. A microphone diaphragm as set forth in claim 14, wherein said self-hardening material comprises a binder material adapted to harden by reaction with a hardener and a hardener for said binder material.

16. A microphone diaphragm as set forth in claim 4, wherein said diaphragm portions, and said spacer means are formed from a thin foil of plastic material having a thickness in the order of 20 microns.

17. A microphone diaphragm as set forth in claim 16, wherein said plastic material is polyvinylchloride.

18. A microphone diaphragm as set forth in claim 1, and including a damping material extending at least partly over said openings.

References Cited UNITED STATES PATENTS 2,003,908 6/1935 Smith 181-32 2,058,208 10/1936 Blattner 18132 2,392,143 1/1946 Graham 179-1155 3,132,713 5/1964 Seeler 181-32 30 KATHLEEN CLAFFY, Primary Examiner R. P. MYERS, Assistant Examiner 

